Sheriff Joe Arpaio said in a statement that deputies had determined Alvares had illegally entered the United States and lived here for most of the last 15 years.

Alvares was working for the past two weeks on a remodeling project at an annex building on the fringe of the plant. While he had to pass through a guard station on the road, he had not passed the heavily armed guards, turnstiles, X-rays, explosive-sensing equipment and other security measures required to get inside the protected area near the nuclear material and control rooms for the plant’s three reactors, McDonald said.